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July 14, 2020 - Posted by

Analyses of organic pollutants are becoming increasingly important, and often with the need to isolate and analyze trace organic compounds from a variety of matrices such as soil, sediment, fruits, and vegetables. In this regard, sample pretreatment constitutes an important step prior to analysis. The purpose of the sample pretreatment step is to selectively isolate or concentrate the analytes of interest from matrix components and present a sample suited for routine analysis by established analytical techniques such as gas chromatography or high-pressure liquid chromatography.

Typical sample pretreatment steps include techniques such as solid-phase extraction, liquid-liquid extraction, solid-liquid extraction, dilution, evaporation, distillation, and the like. Accelerated solvent extraction is a technique used for extracting the analytes of interest from a solid, semisolid, or liquid sample by performing extraction using an organic solvent at elevated temperature and pressure. The elevated pressure also elevates the boiling temperature of the solvent, thereby allowing faster extraction to be conducted at relatively higher temperatures. The benefit of a relatively high-temperature extraction is primarily sped; thus the extraction process is significantly faster than traditional methods such as Soxhlet extraction.

In some samples containing moisture or water such as soil samples or food samples (fruits, vegetables, etc.) an additional step may be needed either before the extraction to remove the moisture from the samples or post-extraction to remove the moisture from the extracted solvent (containing the extracted analytes). Sample drying can be accomplished in several ways such as air drying and oven drying prior to extraction. However, these approaches are not suited when analyzing volatile or semivolatile components as they would be removed from the sample prior to extraction or analysis.

Accelerated solvent extraction (ASE) is an extraction method that is accepted by the U.S. Environmental Protection Agency (US EPA) for extracting solid matrices.1 During the extraction procedure, the solvent is pumped into heated extraction cells under high pressure for a prescribed period of time.2 After extraction, solvent containing analytes are delivered to a collection vial for further cleanup, evaporation, or analysis. While the extraction process is fully automated, additional manual procedures typically using adsorption chromatography are needed to further clean up sample extracts. These methods are often time-consuming, labor-intensive, and use large volumes of solvents.

Thermo Scientific™ Dionex™ ASE™ 350 Accelerated Solvent Extractor is commonly used to extract polycyclic aromatic compounds (PAC) from solid matrices. PACs are a complex class of compounds, include polycyclic aromatic hydrocarbons (PAHs), alkylated polycyclic aromatic hydrocarbons (APAHs), halogenated polycyclic aromatic compounds (HPACs), and heterocyclic aromatic compounds that contain S, O, and N atoms. PAHs, the most common PACs, have been identified as priority compounds by the US EPA.4

The development of ASE extraction methods for PAHs can be traced back to the 1990s.2 Recently, a one-step ASE method that negated the need for adsorption chromatography was reported by Kim et al. to extract PAHs from marine sediments.5 Inspired by the previous work, the Centre for Oil and Gas Research and Development (COGRAD), which is committed to advancing the analytical measurements of oil and gas-related compounds in an ISO-17025 accredited laboratory, decided to further investigate the one-step ASE method for PAHs on two standard reference materials (SRMs). The overarching goal was to verify the suitability of the one-step method and its applicability to improve laboratory efficiency. For more details can be the download of the application note.

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